Domhnall attempted to gain control of the earldom, and sometime after 1405 but before 1411, Domhnall gained control of Dingwall Castle. In the year after the death of the nominal king Robert III of Scotland (1406), in August 1407, Domhnall sent emissaries to England to the heir of the throne, the captive James Stewart. King Henry IV of England sent his own emissaries the following year to negotiate an alliance against Robert Stewart, Duke of Albany, the Guardian of Scotland who was controlling Euphemia and the earldom.

With control over the principal seat of the earldom of Ross and support of the exiled heir to the Scottish throne, in 1411 Domhnall felt strong enough to march against Albany's main northern ally, Alexander Stewart, Earl of Mar. At the Battle of Harlaw Domhnall failed to inflict a decisive victory, and withdrew back to the western highlands. In the aftermath, Albany was able to retake Dingwall and seize control of Easter Ross. In 1415, Euphemia was persuaded by Albany to resign the earldom to his own second son, John Stewart, Earl of Buchan. This action was challenged by Domhnall of Islay, who continued to claim the earldom on behalf of Mariota.

After the return of King James the latter destroyed the power of the Albany Stewarts, executing the Albany's son and successor Murdoch Stewart, Duke of Albany. Domhnall had died in 1423, but Mariota continued to enjoy the support of his successor and her own son, Alexander. Alexander took over her claims, and in 1437 her son was recognized as earl by the king. She died in 1440. She had two known children, Alexander and Mariota.